Sun, January 03, 2021 Turnagain Pass Avalanche Forecast

Sun, January 3rd, 2021

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

1 - Low

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


Travel Advice	Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.	Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.	Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.	Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.	Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches	Natural and human-triggered avalanches unlikely.	Natural avalanches unlikely; human-triggered avalanches possible.	Natural avalanches possible; human-triggered avalanches likely.	Natural avalanches likely; human-triggered avalanches very likely.	Natural and human-triggered avalanches certain.
Avalanche Size and Distribution	Small avalanches in isolated areas or extreme terrain.	Small avalanches in specific areas; or large avalanches in isolated areas.	Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.	Large avalanches in many areas; or very large avalanches in specific areas.	Very large avalanches in many areas.

Avalanche Problem 1

Deep Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

The Dec. 1 rain event formed a crust that is now buried 3-5′ deep and has started to develop weak, faceted snow in some parts of our advisory area. We have found this layer to trend towards weaker strength as you head towards the south end of Turnagain pass, and to be more concerning on the non-motorized (east) side of the road. Closer to Girdwood, we also know this layer has recently produced large avalanches when triggered with explosives during mitigation work. We have found this layer to be losing strength over time, but as the slab above it continues to get stronger, stiffer, and deeper, it is becoming more difficult to trigger an avalanche in this weak layer. This makes for a tricky problem to manage, since although there is a small likelihood of triggering an avalanche in this layer, it will be a large one if you do. The good news is that buried crust only formed up to around 2500’, so upper elevations are not plagued by the same uncertainty as middle elevations. As frustrating as it is, we still need to treat this layer with caution, especially in steep terrain (35 degrees or more) at middle elevations (1000′-2500′).

We will also continue to keep a few Normal Caution issues in mind-

Wind Slabs: After a few days of light winds, these are becoming harder to find and more difficult to trigger. That doesn’t mean you should let your guard down, especially near ridgetops, convex rollovers, or in cross-loaded gullies. We are expecting to see winds pick up later in the day ahead of this next storm, and if that does happen we may see fresh wind slabs forming, which will be easy to trigger. Winds are expected to be slightly stronger near Seattle Ridge during the day today, so pay close attention if you are on the motorized side of the pass.

Cornices: As always, give cornices plenty of room, and limit your time traveling below them. A group traveling near Kickstep reported triggering a cornice fall on Friday.

Sluffs: Be aware of loose snow avalanches moving in steeper terrain wherever there is soft snow at the surface. These can pick up enough momentum to carry a person, and can be particularly dangerous if you are caught above terrain traps like cliffs, rocks, or gullies. In a lot of areas, this soft (weak) snow may become a bigger concern once it gets buried by this next pulse of snow tonight and into tomorrow. More on this to come.

This profile from Lost Lake is similar to the snowpack in the south end of our advisory area. 01.02.2021

The 12/1 rain crust had not started faceting in our snowpits near Surprise Bowl as of yesterday. This layer is a concern in some, but not all places in our advisory area. 01.02.2021

Weather

Sun, January 3rd, 2021

Yesterday: We had another day of clear skies with calm to light winds blowing around 5 mph out of the west at ridgetops. Temperatures reached the upper teens to mid-20’s F in the morning, before gradually dropping to the mid-teens to 20 F overnight.

Today: Clouds will move in as the next storm approaches, with mostly cloudy skies by the end of the day. Winds are expected to remain light, around 5-10 mph out of the east at ridgetops, and increasing this afternoon. High temperatures are expected to be in the mid-teens at upper elevations to low 20’s at lower elevations, and will rise through tonight. Little to no precipitation is expected during the day today.

Tonight: The weather will turn back on tonight into tomorrow, with 2-6″ snow expected at upper elevations by morning and close to a foot of snow by the end of the day tomorrow. Temperatures will hover around the upper teens to mid-20’s F, and we are expecting snow to sea level. Ridgetop winds will pick up to 15-20 mph out of the southeast starting tonight, and stay in that range through tomorrow.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	17	75
Summit Lake (1400′)	2	30
Alyeska Mid (1700′)	16	78

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)*	19	W	5	13
Seattle Ridge (2400′)*	21	VAR	2	9

*Missing data from 6:00 a.m. to 12:00 p.m. on 01.02.2021

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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